1. Field of the Invention
The present invention is directed to the art of wireless telephone networks. More particularly, the present invention is directed to optimizing parameters of radio base stations in a wireless telephone network.
2. Background Information
Cellular and PCS telephone services have enjoyed explosive growth over the last ten years. There is no reason to believe that this growth will not continue for some time. This continued growth creates a great demand for the infrastructure that supports these services. As more and more people begin to use wireless telephones, more and more fixed location base stations must be installed across the landscape to handle the rising demand for wireless traffic.
Each wireless telephone base station has a plurality of transceivers, each connected to a respective antenna. The electromagnetic radiation pattern of each of these antennas defines the coverage area of a “sector.” Each sector in the wireless network has some degree of overlap with one or more nearby sectors, and in the aggregate, the coverage areas of all the sectors in the network define coverage area of the network as a whole.
One difficulty in establishing a network of base stations is that the aggregate coverage provided by the sectors is not perfect. It may have weak spots, or self-interference spots, where wireless telephony functions at a substandard level or it may even have dead spots where no wireless calls can function at all. Such problems can be rectified by optimizing the sectors to attempt to cover the weak and/or dead spots in wireless coverage. Coverage optimization may be accomplished by varying a number of parameters for each sector. One parameter to vary is the azimuth angle at which the antenna for the sector is pointed. Other parameters to vary are the antenna height (moving the antenna higher or lower on its tower, host building, or other supporting structure), the angle of tilt of the antenna (useful in uneven terrain locations), and the amount of power radiated by the antenna. Additionally, the option is also available to substitute a different type of antenna (different model or different manufacturer entirely) in order to obtain better coverage results.
This optimization process is laborious and time consuming. Each time a network engineer wants to change four of the five above-identified parameters of a sector (azimuth, height, tilt, antenna type), someone has to climb up a tower (or other support structure) and physically make an adjustment to the antenna. Only power changes can be made without a need to get at the antenna. Once a parameter has been varied, a fresh set of signal strength measurements must be made by physically driving around the relevant terrain with a measurement device to map out how the parameter change has affected coverage. After analyzing the measurements, another parameter (perhaps for a different sector) can then be varied. This iterative process of vary-measure-vary-measure is repeated over arid over again until an optimum result is obtained. It takes a long time and relies upon highly skilled workers to accomplish.
Thus, what is needed is a labor-saving and time-efficient way to develop optimum coverage-related parameters for sectors of a wireless network.
A wireless telephone often communicates via a number of sectors in succession in the course of a single telephone call via a process called hand-off. In simple terms, one sector will transfer to a neighboring sector the responsibility for handling the wireless telephone call. A hand off may be necessitated because the wireless telephone unit is portable and has moved out of the effective range of the sector that had been heretofore handling the call, or it may be necessitated due to high demand for the limited number of channels that the sector can provide. This is (ideally) done in a seamless manner such that the user of the telephone never notices any discontinuity in service.
In order for call hand offs between sectors to be performed effectively, a number of parameters of the hardware supporting each sector need to be optimized. One parameter is called a “neighbor list.” Each sector has a neighbor list, which is a ranked listing of neighboring sectors to which hand offs may most appropriately be made. The ranking of members in a neighbor list is an important factor in enabling effective hand offs. However, prior art practice is for a network engineer to simply make an educated guess as to which neighboring sectors should be included as members of the neighbor list of a given sector, as well as how to rank the members of the list by importance. Prior art practice does not include a rigorous analysis of how members of a neighbor list should be ranked, or even which neighboring sectors should be included as members of the list.
Another parameter relevant to hand off effectiveness in CDMA wireless networks is “window size.” Window size is a parameter that is set for each sector uniquely. This parameter tells a mobile wireless telephone unit how wide a “window” of code space (in chips) the mobile unit should search through in order to attempt to synchronize with the PN (pseudo noise) sequence of a given sector. As a general rule, it is desirable to set the window size parameter to be the smallest size that will give an acceptable rate of capture of the PN sequence of the sector.
The prior art provides no satisfactory device or process for optimizing choices of window size for the sectors in a network. As with coverage optimization, a network engineer must program the window size parameter at each sector based on his or her best guess as to what should be an optimum value.
A related concept in time division type wireless networks (e.g., GSM, TDMA, iDEN) is the “timing advance” parameter. Timing advance is an analogous concept to the window size parameter of CDMA networks, but is directed to finding an appropriate time slot rather than to code synchronization. The prior art does not provide a suitable way to optimize timing advance, either, leaving network engineers to guess their way to an optimum solution. Such a haphazard optimization technique is not an efficient use of the time of highly skilled workers.
Thus, what is needed is an effective way to optimize hand off timing parameters for sectors in a wireless network.